<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            box-sizing: border-box;
        }
        body{
            background-color: #444;
            color: wheat;
        }
        #result{
            width: 100%;
            height: 100%;
            font-size: 560px;
            font-weight: bolder;
            text-align: center;
        }
        #c{
            position: absolute;
            left: 10px;
            top: 10px;
            width: 100px;
            height: 40px;
            background-color: white;
            font-size: 30px;
            border: 2px solid black;

        }
    </style>
    <script>
        window.onload=()=>{
           let c= document.getElementById("c");
            c.addEventListener("input",()=>{
                document.getElementById("result").innerHTML=c.value;
            });
        }
    </script>
</head>
<body>
    <input id="c"  >
    <div id="result" >我</div>
</body>
</html>